Thermal Abuse Modeling of Li-Ion Cells and Propagation in

Thermal Abuse Modeling of Li-Ion Cells and Propagation in Modules

4th International Symposium on Large Lithium-Ion Battery Technology and Application (with AABC Conference)

In conjunction with the 8th Advanced Automotive Battery Conference

Tampa, Florida

May 13-16, 2008

Gi-Heon Kim, Ahmad Pesaran, and Kandler Smith([email protected])

National Renewable Energy LaboratoryNREL/PR-540-43186

Supported by Vehicle Technologies Program, Energy Storage Technologies

Office of Energy Efficiency and Renewable Energy U.S. Department of Energy

The 4th International Symposium on Large Lithium Ion Battery Technology and ApplicationAABC-08

2

Outline

• Background• Objectives• Simulating Internal Short in a Cell

– Parametric runs– Results

• Propagation in a Module• Summary

Methodology for Understanding Impacts of Battery Design Parameters on Thermal Runaway in Lithium-Ion

Cells/Modules


3

Background• Last year, in LLIBTA-3, we introduced our

approach for modeling Li-ion thermal abuse1

– Chemical reactions at elevated temperatures• SEI decomposition• Negative-solvent reaction• Positive-solvent reaction• Electrolyte decomposition

– Captured real 3-D geometries and boundary conditions– Performed oven heat test simulations– Simulated localized heating – cell internal short– Cell-to-cell propagation in a module

• Balance between discrete heat sources and thermal network• Heat transfer through radiation, conduction, and convection

1G.-H. Kim, A. Pesaran “Analysis of Heat Dissipation in Li-ion Cells & Modules for Modeling of Thermal Runaway,” 3rd Large Lithium Ion Battery Technology and Application, May 2007, Long Beach, CA

Used literature information for graphite–cobalt oxide chemistry


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Thermal Runaway

External Heating

Over-Charging

High Current Charging

Crush

Nail penetration

External Abuse Conditions

External Short

Over-Discharging

Thermal Runaway - Background


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Thermal Runaway

If Heating rate exceeds

Dissipation rate

Internal Short Circuit

Lithium Plating

Causing or Energizing Internal Events or Exothermic Reactions

Decompositions

Electrochemical Reactions

Electrode-ElectrolyteReactions

External Heating

Over-Charging


Crush

Nail penetration


External Short

Over-Discharging



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Thermal Runaway

Leak

Smoke

Gas Venting

If Heating rate exceeds

Dissipation rate

Internal Short Circuit

Lithium Plating

Causing or Energizing Internal Events or Exothermic Reactions

Decompositions

Electrochemical Reactions

Electrode-ElectrolyteReactions

External Heating

Over-Charging


Crush

Nail penetration


External Short

Over-Discharging

Rapid Disassembly

Flames

Thermal Runaway


Focus of the modeling


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• Formulated Exothermic Reactions at elevated temperatures

Reproduce thermal abuse modeling of Li-ion cells provided by Hatchard et al. (J. Electrochem. Soc. 148, 2001);Bob Spotnitz provided insight for reaction formulation

• Extended to multi-dimensional models capturing actual thermal paths and geometries of cells and modules.

Component reactions were fitted to Arrhenius type reactions.Kinetic parameters were determined from ARC/DSC literature data.

A commercial finite-volume method (FVM) solver, FLUENT, was used.

Background - Approach


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Background- 3D Oven Heat Test

P/S: positive/cathode-solvent N/S: negative/anode-solvent

*D18H65: Diameter of 18 mm, Height of 65 mm

Temperature HeatP/S N/S

201

367oC

Small Cell (D18H65)*

Temperature Heat

P/S N/S

198

209oCAlthough oven test is not a highly multidimensional phenomenon, it still demonstrates noticeable spatial distribution, especially in large cells.

Large Cell (D50H90)Average Temp after cell exposed to 155 C.


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• Use the 3D Li-ion battery thermal abuse “reaction” model developed for cells to explore the impact of the location of internal short, its heating rate, and thermal properties of the cell.

• Continue to understand the mechanisms and interactions between heat transfer and chemical reactions during thermal runaway for Li-ion cells and modules.

• Explore the use of the developed methodology to support the design of abuse-tolerant Li-ion battery systems.

Continue to explore thermal abuse behaviors of Li-ion cells and modules that are affected by local conditions of heat and

materials

Objectives of this Study


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Cell Level Thermal Runaway Analysis

• Internal Short Simulation Impact of short location in a cell Impact of thermal property of cell materials Impact of heating rate at short event


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Model Description• MESH Computational grid: 200K Grid size: ~1 mm by 1 mm by 1 mm Max: 2.01 mm3 ; min: 0.31 mm3

½ Model with Symmetry PlaneHot-Spot Localized energy is

released in a short period of time in a very small volume of the core. Initially we assumed 5%

of stored electric energy released

Simulation of details of initial process of short is challenging, but we are trying to predict what happens after shorthappens.

163 mm

54 mm

Heat Sources Exothermic reaction heat No resistive/Joules

heating

Core Material Cylindrically orthotropic properties

Thermal Boundary Conditions Natural/forced convection Gray-body radiation


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Temperature Evolution after a Short

(oC)Internal T External T

0 20 40 60 80 (sec)

Delay between measuring external temperature and internal event, external sensing may be too late.

0 10 20 30 40 50 60 70 80

100

200

300

400

500

600

700

Time(sec)

Tem

pera

utre

(oC

)

T

avg

Tneg term

Tpos term

Tcan surf

T

avg

Tneg term

Tpos term

Tcan surf

Short in the middle of cell

Local internal temperatures of core could exceed 600°C

5% of stored electric energy released in a short time at a small portion of active volume.


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Volumetric Heat Generation after a Short

(W/m3)

0 20 40 60 80 (sec)

Total heat

SEI decomposition

Positive/electrolyte

Negative/electrolyte

(Total and due to various reactions, showing how reactions propagate)5% of stored electric energy released in a short time at a small portion of active volume.


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Impact of the Location of the Short

Initial location of short andthermal paths and material distributions

Propagation pattern Heat release duration

Li-ion Thermal Abuse Reaction Model

Layered structure of electrodes Preferred directions of reaction propagation

5% of stored electric energy released in a short time at a grid point.


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Short Near Exterior Surface vs.Short Near Center of Cell

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

middlenear surfacenear center

Snapshots of temperature distribution at interior (top) and surface (bottom) 38 seconds after short

Total heat released (area under each curve) is about the same for three cases.

Heat dissipation is dependent on the location of heat release and thermal paths.

(oC)


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Short Near Surface vs. Near Center

2 20 38 54

Temperatures

sec

Near center

• Location of short has impact on how heat flows and abuse reactions propagate (e.g., delay in abuse reaction heat release for near-surface case).

Near surface

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

near surfacenear center

Near surfaceNear center

(oC)


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Short Near Bottom of Cell vs.Short Near Top of Cell

Snapshots of temperature distribution at interior (top) and surface (bottom) 25 seconds after short

Total heat released (area under each curve) is about the same for three cases.

Heat dissipation is dependent on the location of heat release and thermal paths.

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

middlenear bottomnear top

(oC)


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Short near top .vs. Short near bottom

near bottom

near topmiddle

2 14 26 38 sec

Temperatures: near-top short

Temperatures: middle short

Heat dissipation is dependent on the location of heat release

and thermal paths.(oC)


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Heat Capacity

Thermal Conductivity

Cp

k50% less 50% more

5% less 5% more

Electrode/current collector thicknesses andrelative amount of component materials

Volumetric heat generationThermal properties of electrode sandwich

Impact of Thermal Properties


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Heat Capacity Impact on Cell Thermal Runaway

Heat Capacity

Cp

5% less 5% more

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)H

eat G

ener

atio

n (k

W)

base5% less5% more

Temperatures

10 20 30 40 secSmall cp

Large cp

Reaction propagation is faster in a cell with smaller heat capacity.

5% of stored electric energy released in a short time at a small portion of active volume.

(oC)


21

Core Thermal Conductivity Impact on Cell Thermal Runaway

Thermal Conductivity

k50% less 50% more

Temperatures

Small k

Large k

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Time(sec)

Hea

t Gen

erat

ion

(kW

)

base50% less50% more

2 14 26 38 sec

Reaction propagation is slower in a cell with smaller thermal conductivity

(oC)


22 4 sec 8 sec 12 sec 16 sec 60 sec

Temperature

20 sec

Impact of Amount of Released HeatHeat: % of cell energy release at a very small volume 1% 5%

No thermal runaway with smaller heat release

Heat dissipates quickly without triggering thermal runaway.

Pattern of initial heat release at short events need to be investigated.

We did an in-depth analysis.

(oC)

2 14 26 38


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Impact of Heating Rate in Short EventsHeat Release at a Short Event is affected by†

• Electrical Resistance of the Short• Cell Power Rate (Power/Energy ratio)• Cell Size (Capacity)

†This is based on our ongoing analysis and the details are beyond scope of this presentation. The next few slides look at a case with high-resistance short. Details of low-resistance case will be presented at other upcoming conferences.


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Quantifying Heat Release at Short Event

Total Heat [W] = Volumetric Heat for Current Production + Heat Release at Short (Short Heat )

Using Electrochemical Cell Model

High-resistance Short Cases (3Ω, 7Ω, 10Ω) Observed from SNL Data

• Short current is determined by the short resistance rather than by the power rate or by the size of a cell.

• Relatively low c-rate for high resistance shorts

• Volumetric heat from current production is small

• Most released heat is local to the short site

0 200 400 600 800 1000 1200 1400 1600 18001

1.5

2

2.5

3

3.5

4

4.5

5

time [sec]

Hea

t [W

]

18650 Cell Spec• 1.35 Ah• 30 mΩ

Total Heat (3Ω)Total Heat (7Ω)Total Heat (10Ω)

Short Heat (3Ω)Short Heat (7Ω)Short Heat (10Ω)


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Thermal Behavior of a Cell at High-Resistance Short Events

0 20 40 60 80 1000

1

2

3

4

5

Rea

ctio

n H

eat [

W]

Time [minute]

3Ω7Ω10Ω

Temperature Reaction Heat

18650 CoO2/graphite30oC ambient, heat transfer coefficient on cell surface (h) = 7 W/m2K

0 20 40 60 80 1000

100

200

300

400

500

600

700

Tem

pera

ture

[o C]

Time [minute]

3Ω7Ω10Ω

7Ω, with h=15W/m2K

Strong natural convection in air

Heat Dissipation vs Heat Release

h=7W/m2K


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Comparison of Thermal BehaviorBetween two High-Resistance Short Events

0 20 40 60 80 1000

0.2

0.4

0.6

0.8

1

Rea

ctio

n H

eat [

W]

Time [minute]

SEI DecompostionNegative/ElectrolytePositive/ElectrolyteNET

0 20 40 60 80 1000

0.2

0.4

0.6

0.8

1R

eact

ion

Hea

t [W

]

Time [minute]

SEI DecompostionNegative/ElectrolytePositive/ElectrolyteNET

7Ω Short

10Ω Short

Temperature Component Reaction Heat

Led to thermal runaway.

Did not lead to thermal runaway.

18650 CoO

2 /graphite Cell

30oC

ambient, (h) = 7 W

/m2K

Can a short have such a high resistance?

(oC)


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Delayed Separator Breakdown With No Cell Runaway (1 amp current)

0

20

40

60

80

100

120

140

160

180

200

0 500 1000 1500 2000Time (s)

Tem

pera

ture

(C)

0

5

10

15

20

25

30

Cel

l Vol

tage

(V)

Pos. Term. TempOCV Voltage

Gen3 ElectrodesCelgard SeparatorEC:EMC\LiPF6

Observed Events Internal Short (may or may not lead to thermal runaway)

(E. Peter Roth and Tom Wunsch)SNL Data: From presentations at DOE’s Advanced Technology Development Meetings

• Short occurred at about 700 sec.• Temperature started to increase and

reached thermal equilibrium at about 160oC.

• Thermal runaway was not observed.

• Heat dissipation appears fast enough.• High resistance short (>5Ω) is likely.

Immediate Separator Failure With PotentialCell Thermal Runaway (1 amp current limit)

0

50

100

150

200

250

300

350

400

450

1250 1270 1290 1310 1330 1350 1370 1390Elapsed Time (sec)

Tem

pera

ture

(C

)

0

2

4

6

8

10

12

14

16

18

20

Cell V

olt

ag

e (

V)

Cell TempVoltage

Gen2 ElectrodesCelgard SeparatorEC:PC:DMC\LiPF6

Short & Thermal Runawayobserved by SNL

• Heat release was much faster than dissipation.• Low resistance short (<<1Ω) is likely

18650 Cells


28

Module-Level Analysis of Cell-to-Cell Thermal Runaway Propagation

How can a module be more resistive to cell-to-cell thermal runaway propagation?

Li-ion Thermal Abuse Reaction Model


29

Background We proposed that Cell-to-Cell Propagation in a module is

a result of the INTERACTION between the distributed chemical sources and the thermal transport network through a module.

• Formulated exothermic chemical reactions of a cell at elevated temperatures.

• Quantified heat transfer among the cells in a module

• We used multi-node lumped approach last year; this year we have looked at 3D approach

Approach for the analysis of this system

Radiation heat transferConduction heat transferConvection heat transfer

dispersed sources thermal network


30

0 10 20 30 40 50 60 70 80 90 10050

100

150

200

250

300

350

400

450

500

1234567891011121314151617181920

Base case (air) Graphite matrix impregnated with PCM

It appears that a very conductive medium may reduce the chance for propagation.NOTE: * PCM/graphite matrix is a highly porous graphite structure that is impregnated with phase-change material (PCM) (based on information from S. Al-Halaj et al.).

0 10 20 30 40 50 60 70 80 90 1000

100

200

300

400

500

600

700

1234567891011121314151617181920

Impact of a Highly Conductive Heat Transfer MediumRather than the air used in the base case (left), a highly conductive PCM/graphite

matrix was used to fill the space between the cells in the module (right).

Example of Multi-node Lumped Module Analysis


31

3D Module Propagation ModelObjective: Developing a 3D cell and module geometry capturing cell-to-cell interconnects

CAD drawing of a 10-cell module(Each cell is in its own individual sleeve) Grid for the 10-cell module

Top view

Bottom view


32

2 seconds apart between each frame

Close Look at Reaction in an Individual Cell in the 10-cell Module


33 5 minutes apart between each frame

Top viewSide view

Reaction Propagation in a Module with 10 Cells in SeriesThe order at which cells go into thermal runaway depends on the cell interconnect configurations.


34

On-going WorkModule-Level Research in ProgressAdding the electrical network modeling

• Impact of thermal transport network + electrical network

6 Parallel, 4 Series


35

• Li-ion thermal abuse reaction chemistry was implemented in a finite-volume 3D cell model to address various design elements. Examined impact of cell design parameters Investigated impact of short location and thermal properties

Some shorts may not lead to thermal runawayHeat dissipation is important, but depending on the amount of heat

release from abuse

• Propagation of abuse reaction through a module was simulated. A complicated balance between the heat transfer network and

dispersed chemical sources Balance is affected by module design parameters such as cell

size, configuration and size of cell-to-cell connectors, and cell-to-cell heat transfer medium

Summary


36

Future Work• Improve model through comparisons with experimental data

from other laboratories• Continue examining the impact of design variables• Address the limitation of the model• Expand the model capability to address various chemistries and

materials, such as iron phosphate• Investigate internal/external short by incorporating an thermally

coupled electrochemistry model into the three-dimensional cell model

• Use the models to investigate the impact of (shut-down) separators

• Work with developers on specific cell and module designs


37

Acknowledgments

Funding is provided by Energy Storage Technologies R&D in the DOE Vehicle Technologies Program, Office of Energy Efficiency and Renewable Energy• Tien Duong• Dave Howell

Documents

Thermal Abuse Modeling of Li-Ion Cells and Propagation in